Getting the GHC Sources

There are two ways to get sources to GHC: download a source distribution, or get the sources directly from our repository using ​git.

Source distributions

A source distribution is a file like ghc-6.12.2-src.tar.bz2, which contains a complete snapshot of the source tree for a particular version of GHC. Source distributions for all versions of GHC are available from the download page.

In addition to fixed releases of GHC, source distributions are also made each night from the current source repository, for both the HEAD and STABLE branches. To download these snapshots, head over to the download page.

Source distributions are easier to build, because we also include the output from running certain external tools like ​Happy, so you don't need to install these tools. See Building/Preparation for details.

Getting a GHC repository using git

Then, if you are on Windows, ensure that git handles line-endings sanely by running:

git config --global core.autocrlf false

A source tree consists of more than one repository: at the top level there is the main GHC repository, and certain subdirectories contain separate git repositories (the full list of git repositories relating to GHC is at Repositories). To get a complete repository tree using git:

Making a local clone

You can make a local clone of a GHC tree with

$ git clone ~/ghc ~/ghc-branch

where ~/ghc is the repository you want to branch and ~/ghc-branch is where you want to put the branch. Then use sync-all as before to branch the rest of the repositories. You can then use sync-all -r <path> to push and pull patches between your two local repository trees.

Getting a branch

The above instructions will get the HEAD - the main trunk of GHC development. There are also branches, from which stable releases are made. The active branches are listed on Repositories.

To get a branch, you need to get from a repo that contains the branch; in particular, local clones of the central repo will normally not include the branches that are in the central repo.

If you already have a GHC tree, then you can switch to another branch with

$ ./sync-all checkout branch-name

Getting a GHC repository from GitHub.com

To get GHC repository from the GitHub.com we recommend to just get GHC source code itself from GitHub and combine this with packages from ​http://darcs.haskell.org. This is easy since sync-all script supports it well.

Pulling new patches

The sync-all script makes it easy to pull new patches. For example, sync-all pull will pull all new patches from the original repository into the repository tree in the current directory.

Tracking the full repository state

The full state of a GHC repository includes the current state of the repositories for all of the GHC boot libraries that are used to to build GHC (see Repositories for a list of the boot libraries). The repositories for these libraries are fetched and updated by the sync-all script. To recored the full repository state (including boot libraries), git submodules could be used, but they are not currently in favor (see The perspective on submodules for some reasons why).

As an alternative to git submodules, the fingerprint.py script in utils/fingerprint/ can create a "fingerprint" to uniquely identify a GHC repository state by recording the current commits of the GHC and boot library repositories. This fingerprint can be used later to restore the state of all repositories to the state captured by the fingerprint.

A fingerprint is created by parsing the output of the sync-all command: ./sync-all log HEAD^.. --pretty=oneline. This command will list each repository along with its commit hash. The fingerprint can be saved for later use. Alternatively, the fingerprint can be created from a Builder log that includes the output of the sync-all command above.

To create a new fingerprint, run the create command in the top level ghc repo. The fingerprint can also be created from a Builder log that contains the appropriate output from the sync-all command by passing the log file to the create command with the -l flag.

This command will read the fingerprint and perform a checkout of the appropriate commit for each repository found in the fingerprint. By default, the restore command will create a new branch in the top level ghc repository and add an entry to git config that sets the new branch's remote to origin. The config options are added so that future sync-all commands will work as expected. Passing the -n flag will cause the fingerprint script not to create a new branch. To "unrestore" a fingerprint, simply use sync-all to checkout the master branch in each repository

$ ./sync-all checkout master

To make the best use of fingerprinting, you need to collect fingerprints for the states you may wish to restore. To ease the automatic collection of fingerprints, the fingerprint.py script allows a -d DIR option that will output a fingerprint to the directory DIR with the current time stamp as a file name. The -g DIR option tells the script to run in the ghc repository pointed to by DIR. These options can be useful for collecting fingerprints as a cron job or on a post-commit hook.